10 Common Mistakes New Mushroom Growers Make (And How to Fix Them)

Starting your journey into mushroom cultivation is exciting, but it's also easy to trip up on avoidable errors that can derail your grow. Whether you're using a monotub, a grow tent, or moving toward sterile mushroom cultivation, understanding the most common mistakes will dramatically increase your success rate—and save you time, money, and frustration.

In this post, we’re pulling back the curtain on the most frequent pitfalls beginner growers face and, more importantly, how to correct them before they cost you your first flush.

1. Skipping Proper Sterilization or Pasteurization

Contaminants love a shortcut. Whether you're working with straw, hardwood pellets, or grain spawn, skipping correct sterilization or pasteurization procedures is a fast track to mold and bacterial contamination.

Fix: Use tried-and-true methods like proper steam sterilization for grain-based substrates or hot water pasteurization for straw. Read our guide on mastering sterile technique here.

2. Overwatering or Underhydrating Your Substrate

Moisture levels are critical. Too wet, and you risk bacterial blooms. Too dry, and your mycelium won’t colonize properly.

Fix: Aim for “field capacity”—squeeze your substrate and only a drop or two of water should come out. If it pours out or feels dry to the touch, adjust accordingly.

3. Improper Air Exchange (CO₂ Buildup)

High CO₂ levels lead to leggy mushrooms with small caps or no fruiting at all. Many new growers forget that fresh air exchange is as important as humidity and temperature.

Fix: Install timed exhaust fans or passive vents for consistent fresh air exchange. If growing in tents or tubs, learn how to balance FAE with humidity retention. For more on this, check out our full breakdown on tent ventilation and air exchange.

4. Using Contaminated Spawn or Culture

It’s tempting to cut corners with spawn sources or reuse cultures too long. But using compromised materials means you're starting behind the curve.

Fix: Always start with clean, tested cultures or grain spawn from a trusted supplier. If you’re making your own, practice sterile technique religiously.

5. Wrong Substrate for the Species

Each gourmet mushroom species has a preferred diet. Lion’s Mane won't thrive on straw alone, and Reishi won’t perform on coffee grounds.

Fix: Match the substrate to the mushroom. Use Masters Mix for fast-fruiting oysters or supplemented sawdust blocks for Shiitake. Learn more in our post on choosing the best substrate for your mushrooms.

6. Lack of Patience During Colonization

Many growers disturb their bags or jars too early, introducing contaminants or stalling growth.

Fix: Let the mycelium do its job. Resist the urge to check daily—wait until full colonization is clearly visible before opening or moving to fruiting.

7. Poor Temperature and Humidity Control

Mushrooms are picky. A few degrees or percentage points off can delay or kill your yield.

Fix: Use hygrometers and temperature sensors. Keep fruiting chambers within optimal ranges—typically 85–95% RH and species-specific temperature zones.

8. Improper Light Exposure

Mushrooms don’t photosynthesize, but they do need light for orientation and proper fruiting. Too much or too little can impact pinning and shape.

Fix: Aim for indirect, 12-hour light cycles using LED or full-spectrum lights. No need to blast them with intense light.

9. Neglecting to Track and Document

Without logging conditions and changes, it’s hard to diagnose problems or repeat successes.

Fix: Keep a grow journal or use a spreadsheet. Track inoculation dates, colonization times, flush sizes, and environmental data.

10. Not Asking for Help Early Enough

Too many new growers suffer in silence or rely on outdated forums.

Fix: Join a trusted mushroom-growing community and ask questions early. At Boxed-In Mushroom Company, we regularly help growers troubleshoot everything from bag contamination to fruiting chamber design. Don’t wait until your grow fails—reach out.

Final Thoughts

Mushroom growing has a learning curve, but avoiding these ten mistakes can help flatten it. Experienced cultivators still face setbacks, but the difference is they know how to respond and adapt quickly.

Ready to level up your mushroom growing skills? We recommend starting with our Sterile vs. Low-Tech Cultivation: Which is Right for You? blog post—it’s packed with practical tips to help you choose the best path for your setup.

Got a mistake you learned the hard way? Share your experience in the comments or tag us with a photo of your grow on social media. We’d love to feature your progress and lessons on our next grower spotlight!